package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

/**
 * @author Fxz
 * @version 1.0
 * @date 2021-07-27 19:24
 */
public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <T> List<T> selectList(String statementid, Object... params) throws Exception {
        //将要完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);
        return (List<T>) list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多!");
        }
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        //使用JDK动态代理为DAO接口生成代理对象并返回
        Object o = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //方法名:findAll
                String methodName = method.getName();
                //获取到类的全限定名
                String className = method.getDeclaringClass().getName();
                String statementId = className+"."+methodName;
                //获取被调用方法的返回值类型
                Type genericReturnType = method.getGenericReturnType();
                //判断是否进行了 泛型类型参数化
                if(genericReturnType instanceof ParameterizedType){
                    List<Object> objects = selectList(statementId, args);
                    return objects;
                }
                return selectOne(statementId,args);
            }
        });
        return (T) o;
    }
}
